Slow product page loading

https://tonerisland.com/product-category/brother/brother-1050/
This page took 25 seconds to load.

When I select a category, then a subcategory, from the category list the resulting page takes a long time to load. Same thing if I just enter a product id.

This site has about 3000 products and is using W3Total Cache, and all images have been optimized. Can you help me discover what the issue is?